Thread: Problem: Functions

Hi everyone.
I have just started learning C and encountered problem with functions.
Here is my code, it compiles successfully, but gives me a runtime error.
So, please, don't just correct a mistake but also could you please explain what caused it. Thanks in advance.

Code:

#include <stdio.h>

void getBalance(int *p_balance);

int main()
{
  
  int balance/*, serviceCharge*/;
  getBalance(&balance);
  
  getchar();
  return 0;
}

void getBalance(int *p_balance)
{
  printf("Welcome to the Cheque Book Balancer\n\n");
  printf("Please enter the current balance: ");
  scanf("%d\n\n", *p_balance);
  printf("*******************************************************");
  printf("Balance forward                                     %d\n", *p_balance);
  printf("*******************************************************");
}

itsme86
thanks, now I understand it perfectly. scanf() needs a location of a variable (p_balance) not an actiual value stored in the variable.

However, when I run corrected code it asks me to input a number and then just stops and does not print anything. Do you know what the problem might be? Thanks

Ok, here is another problem.
Why can't the function call itself if I use pointers. I know that it works with variabels (recursion). If I can't do it this way could you tell me an alternative.

Code:

void updateDeposit(double *p_balance, double *p_deposit, int *p_deposits)
{
  if(*p_deposit>=0){
  printf("Enter amount of deposit: ");
  scanf("%lf", p_deposit);
  *p_balance = *p_balance + *p_deposit;
  *p_deposits = *p_deposits + 1;
  printf("\n");
  printf("Transaction       Debit       Credit         Balance\n");
  printf("****************************************************\n");
  printf("Cheque                        %.2lf           %.2lf\n", *p_deposit, *p_balance);
  printf("****************************************************\n\n");}
  else{
  printf("Invalid amount!\n");
  updateDeposit(*p_balance, *p_deposit, *p_deposits);} 
  
}

A function can call itself if you use pointers.

The problem is that your call is incorrect:

Code:

updateDeposit(*p_balance, *p_deposit, *p_deposits);}

When you use an * outside of a declaration, it means dereference the pointer. You shouldn't have the *'s when you call the function, only in the declaration.

Also, please indent your code properly.

Thanks everyone for help. However here is another problem I got with "while loop". Before even getting input from user it goes straight to "else" and executes whatever is in there. I ran through the program and I don't see where the problem is.

Code:

.
.
.
while((trans = getTrans()) != 'q')
  {
    
    if (trans == 'c' || trans == 'C'){
      updateCheque(&balance, &cheque, &cheques, &bounced);
      transMenu();
    }
    else if(trans == 'd' || trans == 'D'){
      updateDeposit(&balance, &deposit, &deposits);
      transMenu();
    }
    else if(trans == 'w' || trans == 'W'){
      updateWithdrawal(&balance, &withdrawal, &withdrawals);  
      transMenu();
    }
    else
      printf("Invalid selection, enter 'c', 'd', 'w', or 'q': ");    
      
  }
.
.
.
char getTrans()
{
  char ch;
  scanf("%c", &ch);
  return ch;
}

cwr
Also, please indent your code properly.
Is this good enough?

If you don't know what I mean by my previous post, here is the whole program. Run it and see for yourself. So does anyone know what the problem is?

Code:

#include <stdio.h>

void getBalance(double *p_balance);
void transMenu();
char getTrans();
void updateCheque(double *p_balance, double *p_cheque, int *p_cheques, int *p_bounced);
void updateDeposit(double *p_balance, double *p_deposit, int *p_deposits);
void updateWithdrawal(double *p_balance, double *p_withdrawal, int *p_withdrawals);
void updateServiceCharge(double *p_balance, double *p_serviceCharge, int *p_cheques, int *p_bounced, int *p_deposits, int *p_withdrawals);

int main()
{
  int bounced = 0, deposits = 0, cheques = 0, withdrawals = 0;
  double balance, serviceCharge, cheque, deposit, withdrawal;
  char trans;
  getBalance(&balance);
  transMenu();
      
  while((trans = getTrans()) != 'q' && trans !='Q')
  {
    if (trans == 'c' || trans == 'C'){
      updateCheque(&balance, &cheque, &cheques, &bounced);
      transMenu();
    }
    else if(trans == 'd' || trans == 'D'){
      updateDeposit(&balance, &deposit, &deposits);
      transMenu();
    }
    else if(trans == 'w' || trans == 'W'){
      updateWithdrawal(&balance, &withdrawal, &withdrawals);  
      transMenu();
    }
    else
      printf("Invalid input!\tEnter selection (c, d, w, or q): ");
           
  }
  updateServiceCharge(&balance, &serviceCharge, &cheques, &bounced, &deposits, &withdrawals);
  getchar();
  getchar();
  return 0;
}
void updateServiceCharge(double *p_balance, double *p_serviceCharge, int *p_cheques, int *p_bounced, int *p_deposits, int *p_withdrawals)
{
  *p_serviceCharge = (*p_cheques)*1.5+(*p_bounced)*15.0+(*p_deposits)*0.5+(*p_withdrawals)*0.5;
  *p_balance = *p_balance - *p_serviceCharge;
  printf("\n");
  printf("Transaction       Debit       Credit         Balance\n");
  printf("****************************************************\n");
  printf("Cheque            %.2lf                       %.2lf\n", *p_serviceCharge, *p_balance);
  printf("****************************************************\n\n");  
}
void updateWithdrawal(double *p_balance, double *p_withdrawal, int *p_withdrawals)
{
  printf("Enter amount of withdrawal: ");
  scanf("%lf", p_withdrawal);
  if(*p_withdrawal <= *p_balance && *p_withdrawal>=0){
    *p_balance = *p_balance - *p_withdrawal;
    *p_withdrawals = *p_withdrawals + 1;
    printf("\n");
    printf("Transaction       Debit       Credit         Balance\n");
    printf("****************************************************\n");
    printf("Cheque            %.2lf                       %.2lf\n", *p_withdrawal, *p_balance);
    printf("****************************************************\n\n");
  }
  else{
    printf("Invalid amount!\n");
    updateWithdrawal(p_balance, p_withdrawal, p_withdrawals);
  }
}
void updateDeposit(double *p_balance, double *p_deposit, int *p_deposits)
{
    printf("Enter amount of deposit: ");
    scanf("%lf", p_deposit);
  if(*p_deposit>=0){
    *p_balance = *p_balance + *p_deposit;
    *p_deposits = *p_deposits + 1;
    printf("\n");
    printf("Transaction       Debit       Credit         Balance\n");
    printf("****************************************************\n");
    printf("Cheque                        %.2lf           %.2lf\n", *p_deposit, *p_balance);
    printf("****************************************************\n\n");
  }
  else{
    printf("Invalid amount!\n");
    updateDeposit(p_balance, p_deposit, p_deposits);
  }
}
void updateCheque(double *p_balance, double *p_cheque, int *p_cheques, int *p_bounced)
{
  printf("Enter amount of cheque: ");
  scanf("%lf", p_cheque);
  if(*p_cheque<=*p_balance && *p_cheque>0){
    *p_balance = *p_balance - *p_cheque;
    *p_cheques = *p_cheques + 1;
    printf("\n");
    printf("Transaction       Debit       Credit         Balance\n");
    printf("****************************************************\n");
    printf("Cheque            %.2lf                        %.2lf\n", *p_cheque, *p_balance);
    printf("****************************************************\n\n");
  }
  else if(*p_cheque>*p_balance){
    printf("The amount is greater than balance!\n");
    *p_bounced = *p_bounced + 1;
  }
  else{
    printf("Invalid input!\n");
    updateCheque(p_balance, p_cheque, p_cheques, p_bounced);
  }
}

void getBalance(double *p_balance)
{
  printf("Welcome to the Cheque Book Balancer\n\n");
  printf("Please enter the current balance: ");
  scanf("%lf", p_balance);
  printf("\n");
  printf("*******************************************************\n");
  printf("Balance forward                                  %.2lf\n", *p_balance);
  printf("*******************************************************\n\n");
}

char getTrans()
{
  char ch;
  scanf("%c", &ch);
  return ch;
}

void transMenu()
{
  printf("Transaction Menu\n");
  printf("================\n");
  printf("c - Cheque\n");
  printf("d - Deposit\n");
  printf("w - Withdrawal\n");
  printf("q - Quit\n");
  printf("================\n");
  printf("Enter selection (c, d, w, or q): ");
}

Originally Posted by cbastard

Code:

char getTrans()
{
  char ch;
  scanf("%c", &ch);
  return ch;
}

ch is an auto variable.this type of variable are out of scope after the function gettrans finishes.You are returning the value(ch) which does'nt exist anymore.

That function is perfectly valid. It is returning a non-address value so there is no problem with it. If it had been returning a pointer to char and returning the address of ch then there would be a problem.

Ok, but what is the problem with while loop?

try this

Code:

#include <stdio.h>
char getTrans(){
  char ch;
  scanf("%c", &ch);
  return ch;
}
int main() {
   char trans;
   double balance;
   while ( (trans = getTrans() ) != 'q' ) {
      printf( "0x%02x\n", trans );
    }
   return 0;
}

that should show you what's wrong with your loop.
Kurt

True that's useless.
Kurt

Originally Posted by ZuK

try this that should show you what's wrong with your loop.

Ok, it gives me some kind of references or something to characters I enter. How is that suppose to show me what's wrong with the loop?